Systems have been in existence for a number of years for receiving signals from a plurality of television stations and for transmitting these signals through a cable to a subscriber. Each of the television stations provides signals in an individual range of frequencies. For example, the signals from the different television stations may have different frequencies in a range between approximately fifty megahertz (50 MHz) to approximately eight hundred and fifty megahertz (850 MHz). The signals from the different television stations in the frequency range of approximately 50-850 MHz modulate a carrier signal having a suitable carrier frequency.
The television receivers then convert the carrier signals to signals at an intermediate frequency such as approximately forty-four megahertz (44 MHz). These intermediate frequency (IF) signals are then demodulated at the television receivers and the demodulated signals are processed to recover the data signals from the individual ones of the television stations. The processing of the signals occurs on an analog basis.
It is well recognized that the processing of the signals on an analog basis to recover the information in the information signals is not as precise as would ordinarily be desired. The recovery of such information on a precise basis by analog techniques is especially difficult in view of the fact that the information signals are encoded using quadrature amplitude modulation (QAM) with a multitude of amplitude levels.